Electric furnace and control therefor



Ju ne 7, 1932. E. c:v GLITZKE 1,861,472

ELECTRIC FURNACE AND CONTROL THEREFOR Filed Nov. 8, .1928 2 Sheets-Sheet l INVENTOR Ewald C.Glitzke BY Maw ATTORNEY June 7, 1932. E. c. GLITZKE 1,861,472

ELECTRIC FURNACE AND CONTROL THEREFOR Filed Nov. 8, 1928 2 Sheets-Sheet 2 I INVENTOR Ewald Cfililzke B1 21AM 2.

ATTO

Patented June 7, 1932 PATENT OFFICE EWALD C. GLITZKE, OF KANSAS CITY, MISSOURI I ELECTRIC FURNACE AND CONTROL THEREFOR Application filed November 8, 1923.

This invention relates to improvements in electric furnaces and controls therefor, and refers more particularly to an automatically regulated muilie furnace the heating of which is regulated by a timing mechanism whereby a gradual increase in temperature is effected, and a control regulated automatiwhy for limiting the maximum temperature at a predetermined point.

This application is an improvement on my Patent No. 1,650,624, issued November 29, 1927.

Fig. 1 is a perspective front view of the mechanism.

Fig. 2 is a perspective rear view with the back of the timing mechanism removed.

Fig. 3 shows the electric circuit.

Fig. 4 is a detail of the jack or pivoted electrical connection which serves also as a pivot post for the muflle closure.

Referring to the drawings, on a base 1 is mounted a resistance element 2 in the front of which is a compartment 3 in which is positioned a light bulb 4. A muffle or furnace 5 is supported on any convenient and suitable type of standard 6. This muflie has a front closure or door 7 which carries a resistance element 8. A clock 9 or any other suitable timing mechanism is enclosed in the casing 10, the minute hand being pivoted upon the same shaft as the contacting arm 11 in Fig. 3.

Power to the electrical circuit shown in Fig. 3 is supplied through wire connections not shown, with the terminals 12 and 13. The terminal 12 has connection with the heating element or resistance element 14 which is wound within the mufiie by a wire 15. The opposite end of the resistance element 14 communicates through a wire connection 16 with the resistance wire or coil 17 positioned within the casing 2. At different points on the resistance coil are connected the wires 18, 19, 20, 21, 22 and 23. These wires are also connected to the sectors 24,

p 25, 26, 27, 28 and 29 of the rheostat 30 shown in Fig. 2. The binding post 13 has connection through the wire 31 with one terminal 32 of the switch 33. The opposite terminal 34 is connected by a wire 35 to a terminal 36. The terminals 36 and 37 have connections 38 Serial No. 317,982.

and 39 to the light bulb 4 and connections 40 and 41 to the pivot jack 42 which carries or supports the closure 7 of the mufile furnace 5.

Current passing through the pivoted jack also passes through the resistance wire 8 shown in Fig. 1 and Fig. 4 which is swung into the furnace when the mechanism is in operation. Normally the current will pass through the resistance wire 8, as it is of such character that it offers less resistance to the current than the light filament in the light bulb 4. The terminal 37 is also connected by a wire 43 to the contacting arm 11 which is turned by means of the minute hand of the clock and contacts the sectors of the rheostat in its rotation.

In operation, the work which is to be heated is placed in the mufiie and the closure or door shut, at which time the fusing element is inside of the furnace. This fusing element is manufactured from a metal which has a predetermined temperature of fusion. The clock is set so that the maximum resistance is ofiered in the resistance element 17, the current being required to pass through the entire resistance element during the initial stages of heating. As the contacting arm 11 rotates, it successively cuts out sections of the resistance coil and increases the current which is supplied to the heating element 14. When the last element has been cut out by the rotation of the contacting arm 11 the arm rides against a stop such as the winding pin 44 shown in Fig. 2, at which time the entire current is supplied to the heating element of the muffle.

When the temperature of the muflie reaches the temperature at which the element 8 fuses, the current will then pass through the wires 38 and 39, lighting the bulb 4 and indicating to the operator that the desired temperature has been reached and the element fused. The switch 33 can then be pulled and the mufile allowed to cool.

While the mechanism has been designed for any purpose in which a controlled temperature is desired in an electric furnace, it is particularly adapted to dental use in the fusing of porcelain where accurate temperature is essential and proper heating conditions maintained. The automatic timing mechanism which operates the rheostat steps up the muflie temperature at regular, definite intervals timed by the clock. This regulation of the heating materially increases the life of the heating element by preventing too rapid heating and overheating of the element The invention, while drawn to an automatic timing mechanism, contemplates also the manual advancement of the rheostat, as the clock has been chosen merely as a convenient method of automatic control.

A further advantage in the mechanism lies in the complete automatic control which entirely eliminates the necessity of an operator, thus saving the operators time. The work can be placed in the muflie and no attention given to it until the current is shut off when the light bulb indicates that the desired temperature has been reached.

A further advantage is the accuracy of regulation of the maximum temperature which is an essential factor in the proper heating and fusion of porcelain and is an important factor with other types of work where a definite maximum temperature is essential. The regulation of maximum tem perature prevents overheating of the muffle and overfusing or overheating of material undergoing treatment. Thus the life of the muffle is materially lengthened and the results obtained from this accurate control considerably improved It has been found where a pyrometer 1S employed that constant irregularities and variations are encountered, and variations occur dueto the age of the mechanism, particularly the muffle furnace. The age of the furnace and associated apparatus does not produce such variations in temperature with the present mechanism because the furnace temperatures are always regulated by a fixed fusion temperature which is the temperature at which the fusing element melts, and is accurate despite the conditions or age of the mu-file furnace and its associated apparatus.

The simplicity of the mechanism is also of importance as there is no delicate instrument such as apyrometer to get out of order, and the three-unit construction comprising rheostat, muflie and resistance element, are independent andreplaceable without disturbing either of the associated elements or its parts.

\Vhile a clock has been shown 'as the timing'mechanism or timing element for periodically eliminating a portion of the resistance coil and thereby increasing the current supplied to the muffle, the invention contem plates any type of motive force, such as a motor or other means for regulating the periodic changesof the rheostat to increase or decrease the current to the muffle.

When the element 8 within the muflle' has fused and the current is passing through the bulb 4, this reduction in current produced b the resistance of the filament reduces su ciently the current supplied to the heating element 14 to immediately decrease the current to an amount insuflicient to heat the mufile to any considerable degree.

I claim as my invention:

1. An automatic control assembly for electric furnaces, constituting a three-unit construction comprising a mufiie, a resistance element and a timing mechanism, a rheostat functioned by the timing mechanism adapted to periodically increase the current and heat supplied to the muflle, and fusiblemeans inthe muflie adapted to break the circuit when the temperature in the muffle reaches a predetermined maximum point.

2. A three-unit control assembly for electric furnaces, constituting a muflle having a fusible element therein adapted to break the circuit when a predetermined maximum temperature has been reached, a resistance element and a timing mechanism, an electric circuit communicating between the units whereby the resistance elements are periodically eliminated and current supplied to the mufile progressively increased to the fusing temperature of the fusible element and then automatically reduced said fusible element preventing the temperature from increasing beyond a predetermined point.

3. A three-unit control assembly for electric furnaces constituting a muflle having a fusible element therein, resistance elements and a timing mechanism, an electric circuit communicating between the units whereby the resistance elements are periodically eliminated and current supplied to the mufile progressively increased to the fusing temperature of the fusing element, said fusing element preventing excessive temperatures, a signal light connected in the circuit and adapted to light with the fusing of the fusible element.

EVVALD C. GLITZKE. 

